The proposed research seeks to develop the chemical principles governing iron bioavailability in humans by examining in vitro the digestive chemistry of food iron. Iron deficiency is a highly prevalent nutritional problem in both developing and industrialized societies, the problem is seldom the amount of iron in diets but rather its bioavailability. I propose to delineate the chemical principles that govern food iron availability under digestive conditions. Foods, beverages, and additives are subjected to an in vitro digestion that simulates human digestion. The incubation mixture is then separated by centrifugation into the soluble and residue bound iron fractions. The following questions delineate our overall approach to the problem. I. What are the physical associations and chemical reactivities of soluble iron species? II. What are the iron exchange characteristics of the digestive residue (sediment)? III. Can simple model systems mimic the digestive iron chemistry phenomena? IV. What are the effects of foods, components and combinations on in vitro iron solubilization and chemical reactivity? V. How does extent of mobilization and the chemical reactivity of soluble iron species correlate with bioavailability? VI. Can the information obtained on iron reactivity fractions, soluble effectors and residue binding characteristics be summarized by computer generated graphical representations with predictive capabilities? VII. How can these methodologies be applied to nutritional problems of national and international significance?